1. Field of the Invention
The present invention relates to a gate valve and, more particularly, to improvements in which an actuator is provided between a pair of valve plates, and in which the valve plates are moved in the axial direction by the operation of the actuator so that the sealing operation can be achieved with a small sealing force, thereby allowing a reduction in the rigidity of the valve plates and a valve rod.
2. Description of the Related Art
Conventionally, structures of non-sliding vacuum gate valves disclosed in, for example, Japanese Unexamined Patent Application Publication Nos. 8-42715 and 10-110834, which are not shown, are generally adopted.
In non-sliding vacuum gate valves constructed in the conventional manner, the following problems occur:
Since one valve plate is vertically moved to open and close a valve of an opening of a valve casing, if the relationship between the pressure P0, on the side of a valve plate 1 and the pressure P1 on the side of a valve casing 50 satisfy the condition P1 greater than P0, the pressure P1, is applied to an area Sa surrounded by sealing member 3 such that the valve plate 1 separates from a valve seat 4 as shown in FIG. 1.
A force f, where f=(P1xe2x88x92P0)xc2x7Sa, is applied and it becomes necessary to add the value f to the sealing force, which is originally required, in order to achieve the operating force required for the valve closing (sealing) operation. Therefore, the valve plate and the valve-plate driving section are required to have a large weight and high rigidity, and consequently, the structure of the gate valve itself becomes so large and complicated that it is difficult to manufacture at a low cost.
The present invention has been made to solve the above problems. Accordingly, it is an object of the present invention to provide a gate valve in which a pair of valve plates have an actuator therebetween to move the valve plates in the axial direction by the operation thereof, thereby performing a sealing operation with a small sealing force, and allowing a reduction in the rigidity of the valve plates and a valve rod.
A gate valve according to the present invention comprises: a first valve plate having a valve openings; a second valve plate connected to the first valve plate via expandable body; and an actuator provided between the first valve plate and the second valve plate, wherein, preferably, the first valve plate is moved by the operation of the actuator, the first valve plate is provided with a valve rod, the second valve plate is provided with the valve rod, the valve rod is located at the center of the expandable body in the axial direction, the actuator comprises an air cylinder, the actuator is surrounded by dustproof bellows provided between the valve plates, the air cylinder comprises a piston, a piston rod, and a cylinder, which are provided at the valve plates, a pressure medium is supplied to a space formed between the piston and the cylinder, and the first valve plate is provided with first sealing member. The gate valve according to the present invention further comprises: a valve casing for enclosing the valve plates in a manner which allows them to be freely moved; a first valve seat formed in a first opening of the valve casing, with which the first sealing member come into contact; and a first stopper formed in the second opening of the valve casing, with which the second valve plate comes into contact. A gate valve according to the present invention, further comprises: a valve casing for enclosing the valve plates in a manner which allows them to be freely moved; a first sealing member formed in the first opening of the valve casing, with which the first valve plate comes into contact; and a first stopper formed in the second opening of the valve casing, with which the second valve plate comes into contact. A gate valve according to the present invention, further comprises: a valve casing for enclosing the valve plates in a manner which allows them to be freely moved; a first valve seat formed in the first opening of the valve casing, with which the first sealing member comes into contact; and a second stopper which protrudes from the second valve plate, which is located on the inside or outside of the expandable body, and which comes into contact with the valve casing on the side of the first opening. A gate valve according to the present invention, further comprises: a valve casing for enclosing the valve plates in a manner which allows it to be freely moved; a first valve seat formed in the first opening of the valve casing, with which the first sealing member comes into contact; and a second stopper which extends to the inner wall of the valve casing, which is located on the outside of the expandable body, and which comes into contact with the first valve plate.